Spark-plug



T. G. McDOUGAL.

SPARK PLUG.

APPLICATION FILED NOV-22, 1919.

1,386,883, 7 Patented Aug. 9, 1921.

} GLAZED UNGLHZED M I gwvenFoz fr 51% 411A CIH'OZ'HQIJQ/ UNITED STATESPATENT OFFICE.

TAINE G. MCDOUGAL, OF FLINT, :MICHIGAN, ASSIGNOR T0 CHAMPION IGNITION.GOM- PANY, OF FLINT, MICHIGAN, A CORPORATION OF MICHIGAN.

SPARK-PLUG.

Application filed November 22, 1919.

T 0 all whom it may concern:

Be it known that I, TAINE G. MoDooGAL, a citizen of the United States,and a resident of Flint, county of Genesee, and State of Michigan, haveinvented certain new and useful Improvements in Spark-Plugs, of whichthe following'is a full, clear, concise, and exact-description, such aswill enable others skilled in the art to which the invention relates tomake and use the same, reference being made therein to the accompanyingdrawings, which form a part of this specification.

Spark plug porcelains as heretofore constructed have been glazed overthose areas which contact with the associated shell or retaining parts,with the result, I have discovered, that considerable electrical leakagetakes place between the central electrode and the shell. I have alsodiscovered that the glaze is a better conductor, particularly at hightemperatures, than is the body of the porcelain, These discoveries Imake use of,v

in accordance with the present invention, by providing over the areas ofcontact of the porcelain with the shell or other metallic parts a beltor belts of unglazcd surface, whereby electrical connection of the shellwith the central electrode, both at top and bottom, is more effectivelybroken.

While the unglazed belt or belts may be formed in different ways, andwhile the position and extent of the unglaze'd area is subject tovariation, I prefer to simply guard a single wide belt extending overthe zone or zones of contact of the porcelain with the shell orretaining elements in such manner as to protect it from the glazespray,in the glazing operation. By proceeding in this manner, the objectssought are accomplished with substantially no increase in expense.

In the drawings:

Figure 1 is a central vertical section showing one well known typeofplugto which the invention is applicable. It will be understood that theparticular plug selected is merely by way of example; in other words,

the invention may be applied equally well to the other types of plugsiii common use.

Fig. 2 is an elevation of the porcelain and central electrode whichappears in Fig. 1.

The metal shell 1, in the construction shown, is provided with ashoulder 2, on which the central rib 3 of the porcelain bears,

Specification of Letters Patent.

- ture,

Patented Aug. 9, 1921.

Serial No. 339,830.

a washer 4 ordinarily being interposed. Metalhcreta nmg means, which inthis instance in the form of a pressed or spun flange 5 and aninterposed sealing washer 6,

bearson the upper surface of the rib 3 to securely hold the porcelain inplace. The usual central electrode appears at 7.

In accordance with the preferred applicatlon of the invention, I protectthe surface of the rib and the adjoining surface ofthe upper and lowerend portions of the porcelain so that when the glazing liquid is sprayedthereon an unglazed belt, wide enough to extend from some distance belowthe shoulder 2 to some distance above the flange 5, is retained, therebyeliminating contact between the metal shell or retaining elements andthe glaze. The actual construction may of course be varied but theunglazed gap or gaps should be interposed between the shell and both theupper and the lower end of the electrode.

In the subjoined claims, I use the expression shell structure in a sensesuch as to include both a one-piece shell such as shown. and a shellbuilt up from two or more members or elements.

I claim:

' 1. A spark plug including ashell struca glazed porcelain, retainingmeans carried by said shell structure for engaging the porcelain, anelectrode passing through the porcelain and projecting at each endthereof, there being an unglazed portion between the retaining means andeach end of said porcelain to more completely break electricalconnection between the shell and both ends of the electrode.

2. A spark plug including a shell structure, a glazed porcelain, anelectrode passing through the porcelain and projecting at eachendthereof, the end portions of the porcelain being glazed throughoutthe greater part of their length, and the intermediate portion of theporcelain being unglazed over a wide belt wherein it contacts with theshell structure and "retaining means car: ied by said shell structurefor engaging onlyof said porcelain.-

3. A spark plug porcelain pierced from end to end to receive a centralelectrode and having a circumferential rib intermediate its length, saidrib being unglazed over its peripheral and end surfaces, and theporcelain being otherwise glazed substantially throughout its entireouter surface, said unglazed surfaces being adapted to prevent thecontact of the retaining means with said glazed surfaces, when in use.

a. A porcelain insulator for spark plugs having an aperture to receivean electrode, said insulator having its end portions glazed and havingan unglazed portion between its ends, said unglazed portion beingadapted to be engaged by retaining means and to prevent the contact ofthe latter with said glazed portions.

5. In a device of the class described, a porcelain insulator providedwith means for receiving an electrical conductor and having glazed andunglazed portions thereon, and a support for said insulator engagingsaid unglazed portion only.

In testimony whereof I afiix my signature.

TAINE Gr. MGDOUGAL.

